Leeds began the second half of the Super League season with easily their most significant win so far, denying Warrington the chance to go top of the table and in the process climbing into the top six for the first time since February. But the points came at a potentially heavy cost for Jamie Peacock, who had to be helped off in the seventh minute with a knee injury that seems certain to prevent him leading England in the one-off international against France next month – and will rule him out for months, if the Rhinos' worst fears are confirmed.

"He's in a brace and we're going to have him scanned on Monday but at this stage it doesn't look too flash," said their coach, Brian McClennan, hinting at serious ligament damage. Peacock, who has only recently returned from sprained ligaments in his foot, suffered the injury as he made a desperate try-saving tackle on Adrian Morley, the veteran Warrington prop who must now be the favourite to benefit from his misfortune by taking over the captaincy.

Leeds responded impressively to inflict Warrington's fourth defeat of the season, but the Rhinos' main concern regarding Peacock will be parochial rather than patriotic, with a tough Challenge Cup quarter-final against Wigan looming in less than a fortnight.

Warrington came into the game in far better form than the Rhinos, having scored 60 points in each of their last two matches, but were forced to make two significant changes as Michael Monaghan and Richie Myler were both ruled out. Their coach, Tony Smith, revealed that Myler will be out for around six weeks with medial knee ligament damage, denying him the chance to repeat his prolific performance for England in France last year. The early indications were that the Wolves would not be adversely affected here, as they dominated the opening exchanges and took a 6-0 lead when Matt King touched down a delicate kick by Simon Grix. Leeds had been horribly disorganised, with their captain Kevin Sinfield making uncharacteristic errors, and suffered the additional blow of losing Peacock.

But they seized their first attacking chance, presented by a Lee Briers fumble, to pull level when Carl Ablett steamed on to Danny McGuire's short pass, and suddenly began to look more like the team who have won the last three Grand Finals. They went ahead for the first time in the 27th minute when Brent Webb's pass caught Chris Hicks out of position, and Ryan Hall finished clinically on the left.

Sinfield curled over an excellent conversion, and the Rhinos opened up a 12-point gap four minutes into the second half when Keith Senior charged through Briers' weak attempted tackle and found Webb supporting on his inside. By this stage Warrington had lost King, who had taken a while to get up after a heavy tackle late in the first half.

They remained in the contest until Lee Smith pounced on a loose pass deep inside the Rhinos half and sprinted 60 yards, inducing a professional foul by Hicks for which the Australian was sent to the sin-bin. Sinfield kicked the resulting penalty, and the influential Ablett then sent McGuire scampering over for a fourth Rhinos try that removed any doubt about the outcome, despite late Warrington tries from Grix and the outstanding Ben Harrison.